The invention generally relates to overriding a primary control subsystem of a downhole tool.
Downhole tools typically are used in a well to perform functions related to the drilling, testing and completion of the well, in addition to functions related to monitoring and controlling downhole production or injection after the well's completion. Such tools include flow control valves, isolation valves, circulation valves, perforating guns, sleeve valves, ball valves, etc. A typical downhole tool contains a primary control subsystem that responds to control stimuli, such hydraulic pressure, fluid pulses, electrical signals, etc. for purposes of operating the tool. As an example, a primary control subsystem for a downhole tool may contain a hydraulic circuit that actuates the tool in response to hydraulic pressure that is communicated downhole via one or more hydraulic lines.
It is possible that during the lifetime of a downhole tool, the tool's primary control subsystem may fail. Conventional corrective actions, such as intervening, plugging or perforating, may be used when the primary control subsystem fails.
Intervening typically involves deploying a mechanical tool into the well on a slick line or coiled tubing to engage the downhole tool and provide an actuation force. Plugging involves placing a plug in the wellbore beneath the downhole tool and applying pressure to the plugged well, which actuates the tool. Perforating may be another option that is used, for example, when the primary control subsystem fails. For example, the tool may be a flow control valve that is part of a tubing string and controls fluid communication between the string's central passageway and the annulus of the well. More specifically, the valve may have failed in a closed position, and a perforating gun may be run downhole and used to perforate the tubing string for purposes of re-establishing a flow path between the annulus and the central passageway.